As of the date of this report, over 25 patients have been evaluated for idiopathic anaphylaxis. All patients were admitted to the inpatient unit and underwent a bone marrow procedure for aspirates and biopsies in an attempt to elucidate the etiology and evaluate the pathogenesis of their disease. Patients also had research blood drawn along with routine labs. In collaboration with the NIH Clinical Center's myeloid core facility, we were able to assess all the patient bone marrow aspirates and biopsies obtained based on the current WHO criteria to rule out the diagnosis of systemic mastocytosis. Mast cells derived from peripheral mononuclear cells were cultured for mast cell growth and activation studies in comparison to mast cells from healthy volunteers. Preliminary data suggests that in some patients with anaphylaxis, their mast cells are more reactive. Six subjects have been enrolled in the randomized treatment protocol with omalizumab (09-I-0129). Data has not yet been analyzed.